1. Field of the Invention
The present invention generally relates to methods for limiting or controlling the foam above the top surface of a liquid. More particularly, the invention is directed to a methods utilizing ultrasonic energy to control foam by breaking the surface tension of the bubbles creating the foam above the liquid. The invention has application in the filling of containers with carbonated beverages, including soft drinks and beer, where the control or elimination of foam can enable higher production speeds, improved yields, reduced energy costs and improved net content capabilities. Other uses include foam control during container filing with non-carbonated liquids including juices, teas, sports drinks, liquid cleaners and wine. The present invention is not restricted by the material used in the container construction, which can include materials such as aluminum, steel, plastics, glass and composites. Other uses also include foam reduction from continuous streams of emulsions, suspensions, and high viscosity liquids used during the production of various commercial products.
2. Description of the Prior Art
For reasons of economy, commercial containers are not sized substantially larger than as required for accommodation of the contents. Thus, during filing operations it is common for some amount of liquid in the form of foam to bubble over the top of the container prior to the container being capped or sealed. The product loss can reach as high as ten percent, which translates into higher cost for the consumer or lower profitability for the bottler, or both. To reduce this product loss, some filing lines include a dwell station that allows for the product foam in a recently filled container to settle prior to top sealing. Other filing lines include a short suction pipe adapted to be introduced into the container to be sealed, and a suction system whereby the foam over the top surface of the liquid is removed and optionally recycled into the product reservoir. Some filing lines may also use blast nozzles for blowing any drops and residual foam from the surfaces to be sealed or bonded. Some filling lines reduce the temperature of the liquid at the mixing tanks or other reservoirs to reduce foaming. Other filled products are purposefully overfilled to compensate for lost product in the form of foam and thereby achieve the desired net fill volume, which results in undesirable product loss.
Matzner, U.S. Pat. No. 4,295,502 discloses that foam can be collapsed in place by subjecting the foam structure to high-frequency wave radiation from a source spaced above the liquid. The portion of liquid forming the foam then again becomes part of the liquid content of the container, rather than being wasted. Sound waves, primarily those above the sonic range, are used with the high-frequency range in the neighborhood of 20,000 Hz. The ultrasonic radiation is directed toward the top of the liquid. This results in a concentration of the radiation on the foam structure. Matzner reports particularly good results are obtained in the destruction of foam when a plurality of overlapping ultrasonic wave fields extending in substantially the same direction are caused to act on the foam structure. Matzner discloses using eight parallel ultrasonic wave fields radiating into the foam by an appropriately designed horn or sonotrode. After an exposure time of just 0.2 to 0.3 seconds the foam is reportedly destroyed to an extent not usually attainable by a suction arrangement.
Matzner additionally indicates that when sonotrodes are used for the radiation of ultrasonic waves, it is advantageous to combine a plurality of sonotrodes into a bank of sonotrodes or into an aggregate sonotrode. The individual sonotrodes are advantageously constructed as pins and arranged parallel to one another on a metal block to permit them to radiate the individual ultrasonic wave fields side by side and close together into the foam. In order that the foam layer over the liquid may be fully covered even by a focused radiation field, Matzner indicates it is advisable to adapt the aggregate sonotrode to the cross-sectional configuration of the container in the area of the liquid level.
While the exposure time of 0.2 or 0.3 seconds seems to be very short, the fact remains that current filling lines often run at speeds of between 800 and 2000 containers per minute. Thus, one following the Matzner disclosure would necessarily have to provide a series of such aggregate sonotrodes, or an elongated sonotrode array, aligned along the filling line so that each container traveled under serially under several aggregate sonotrodes in order to achieve the required exposure time. Thus there is an unsatisfied need for an operating single defoaming sonotrode that can effectively eliminate foam from the top of a container of liquid while the container is traveling on a high-speed filing line.
Continuous streams of emulsions, suspensions, and moderate to high viscosity liquids are used during the production of various commercial products including paper slurries, photographic products, mineral ores, and waste stream management. The continuous streams can develop a layer of froth or foam on top of a liquid. In some processes, the foam or froth is used as a separating mechanism to concentrate and separate one portion of the continuous stream from the remainder of the stream. After separation of the foam or froth containing the separated portion of the stream, it can become desirable to return much of the liquid fraction forming the froth or foam to the continuous stream. In other processes, the presence of the froth or foam is undesirable and performs no useful function whatsoever. The foam and froth have been known to be reduced by placing ultrasonic transducers in or under the continuous stream to assist in the degasifying of the stream. Examples are to be found in Jacke, U.S. Pat. No. 3,229,448; Philips et al., U.S. Pat. No. 6,210,470; and Varadaraj, U.S. Pat. No. 6,590,000. It has been recognized that in some cases it is desirable to physically separate the ultrasonic transducer from the stream, but there is an unsatisfied need for a single defoaming sonotrode operating so as to effectively eliminate foam from the top of a continuous stream of liquid while the liquid is traveling at a high rate of speed.